Journal of Science and Technique
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VERIFYING MATERIAL MODELS OF CONCRETE AND REINFORCEMENT IN LS-DYNA SOFTWARE BY THE EXPERIMENTS
Get PDFThis article presents research and evaluation of a number of concrete and reinforced material models commonly used in LS-DYNA to simulate reinforced concrete structures subjected to explosion pressures. Based on that, the selections of a suitable material model with the priority input for modeling are the basic parameters of the materials. Through the simulation results and the field explosion experimental data, the verifications and evaluations of the responses of the selected material models are conducted. The method developed for the simulation of the behaviour of the reinforced concrete slabs under explosions using LS-DYNA is also presented in this article
INTERACTION BETWEEN A BEYOND-BAND DISCRETE SOLITON AND A DIRAC SOLITON IN BINARY WAVEGUIDE ARRAYS
Get PDFWe investigate the intricate interactions between a beyond-band discrete soliton (BBDS) and Dirac soliton in a binary waveguide array (BWA). Through comprehensive analysis, we demonstrate that the behavior of these soliton interactions remains largely unaffected by the presence of central peaks or dips at the center of each soliton, or the initial phase differences between them. Our research highlights the critical role of the BBDS intensity in determining the nature of its interaction with Dirac solitons. We reveal that low-intensity BBDS exhibit consistent attraction towards Dirac solitons across multiple encounters, while high-intensity BBDSs show an initial phase of attraction followed by a repulsion phase, causing a subsequent divergence. These findings not only enhance our understanding of soliton interactions on a fundamental level but also set the stage for the development of innovative optical communication and signal processing technologies leveraging the distinctive properties of BBDSs and Dirac solitons
FORMATION MECHANISM AND SYNTHESIS OF HIGHLY CRYSTALLINE POROUS ZnO SUPERSPHERES VIA SOL-GEL PROCESS: EVOLUTION FROM INTACT HOLLOW STRUCTURES TO POLLEN-LIKE MORPHOLOGIES
Get PDFThe synthesis of hollow and porous (HP) ZnO superspheres with intact hollow structures is crucial for various applications, yet it poses significant challenges. This article explores the fundamental aspects of preparing highly crystalline HP ZnO superspheres via a sol-gel process, elucidating the synthetic strategy, formation mechanism, and subsequent utilization for generating pollen-like ZnO superstructures. Under solvothermal conditions at 200°C, employing zinc acetate (0.065 M) in diethylene glycol with varying molar ratios of H2O/Zn, a range of ZnO particles and superspheres were synthesized. Within a molar ratio range of 2 - 4, initial nanoparticles self-assembled into solid and porous (SP) superspheres, evolving dominantly towards or along the c-axis, resulting in HP superspheres with intact hollow structures. Conversely, molar ratios of 6 - 20 yielded only separate nanocrystals instead of superspheres. The critical role of the H2O/Zn molar ratio in forming HP superstructures with intact hollows was highlighted, controlling Ostwald ripening and outward diffusion rates, with a molar ratio of 2 identified as a prerequisite for intact HP superspheres. The resultant intact HP superspheres exhibited intense and sharp band gap emission at 389 nm, indicating potential for optoelectronic applications. Furthermore, the study introduces pollen-like ZnO colloids derived from these intact HP ZnO superspheres, offering stable dispersion. Crystal growth predominantly occurred along the outward-oriented c-axis. The intact HP ZnO superspheres serve as a promising template system for biomimetic pollen-like ZnO superstructures
PRELIMINARY EVALUATIONS OF AIR TEMPERATURE EFFECTS ON THE RESPONSE OF SEISMICALLY ISOLATED BRIDGES EMPLOYING ELASTOMERIC BEARINGS
Get PDFLaminated rubber bearing is a common seismic protection device for bridge structures based on its high vertical stiffness, low horizontal and rotational stiffness, and significant lateral restoring capacity. However, the mechanical behavior of elastomers, particularly the material's shear stiffness, is significantly influenced by variations in air temperature. The cyclic behavior of elastomeric isolators is affected by variations in air temperature and this is considered by current seismic codes through requiring upper and lower bound analysis using relevant modification factors. As a result, it significantly impacts the seismic responses of structures employing laminate rubber isolators. However, this aspect is not frequently considered when designing seismic isolation in most locations. This article aims to evaluate the effect of air temperature on the seismic response of isolated bridges. A parametric study, with varying temperature conduction, is carried out. The responses of a seismically isolated bridge are evaluated by the peak value of lateral force and displacement. Results indicate that air temperature has considerable effects on the behavior of rubber isolators and seismic responses of isolated bridges
DENOISING THE SHOCKWAVE PRESSURE SIGNAL OF UNDERWATER EXPLOSION BASED ON EMD-CEEMDAN IN CONSIDERATION OF THE SIGNAL CURVE CURVATURE
Get PDFThe measured signal of shockwave pressure of underwater explosion is usually disturbed by many objective factors such as the disturbance of the environment surrounding the sensors, the complexity of wave propagation and wave reflection in complex environments, the formation and fluctuation of air bubbles, especially analog signals always have noise due to the influence of electronic noise from the A/D converter and circuit board error embedded in measuring devices, etc. These are the main causes of initial waveform distortion, obscuring important characteristics of the signal, and making it difficult to use and further analyze underwater explosion shockwave pressure. Based on two algorithms Empirical Mode Decomposition (EMD) and Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN), this article combines the two algorithms above into one denoising model called EMD-CEEMDAN model with Python codes. Three evaluation criteria such as the average curvature of the signal curve, signal-to-noise ratio (SNR) and mean squared error (MSE) are applied to establish the most suitable denoising model. Applying this model to experimentally measured signal of underwater explosion shockwave pressure, the results show that high-frequency noise is eliminated, the denoised signal is transformed into a typically smooth explosion signal while its peak pressure value differs only about 2% from that of the initial signal
A HIGH-ENERGY ANODE FOR SODIUM-ION BATTERIES BASED ON SODIUM MOLYBDATE MATERIALS
Get PDFIn this study, sodium molybdate (Na2MoO4) was synthesized by a conventional solid-state reaction method. Crystal structure and morphology of the Na2MoO4 material were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The Na2MoO4 material was utilized to fabricate CR2032-type coin cells, and later evaluated for its electrochemical characteristic. The electrochemical characteristics of Na2MoO4 were evaluated through cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charging-discharging at different current densities on a NEWARE battery testing system (BTS). The results of studying the electrochemical properties of Na2MoO4 material has shown that it has pretty good electrochemical properties. In particular, the Na2MoO4 electrode material has achieved an outstanding specific capacity of about 420 mAh.g-1 at 0.1 C within the voltage range from 0.2 to 2.2 V. The Na2MoO4 material exhibited a quite good cycling performance, it is able to remains up to 80% specific capacity over 50 cycles at the current density of 0.1 C. In addition, when charge/discharge at the high current density of 1 C, it has retained a specific capacity of about 240 mAh.g-1. The results suggest that the Na2MoO4 material is a promising anode for sodium-ion batteries
MULTI-SENSOR CAMERA MODEL FOR CONTROLLING COORDINATES OF POINTS ON THE SURFACE OF TELESCOPES
Get PDFA new optoelectronic system for measuring the reflective mirror surface distortion of large telescopes is discussed in this study. This system comprises a multi-matrix structure of CMOS sensors, each sensor responsible for capturing an image of a control point on the mirror surface through a common objective. Simulation and calculation studies show that during operation, the position of the multi-sensor camera on the supporting ring is determined by control points on the telescope surface. The more control points, the higher the accuracy of the calculations. Simulation results indicate that the camera position error falls within acceptable limits when using 5 or more control points. Experimental results show that when calculating simultaneously with 3 control points, the error in determining the angular position of the camera reaches a value of = 0.302 arc minutes, which is 2 - 2.5 times smaller than when calculating with only one control point
RESEARCH ON APPLICATION OF FINITE ELEMENT METHOD TO ANALYZE LOAD TRANSFER EFFICIENCY ACCORDING TO DEFLECTION OF AIRPORT RIGID PAVEMENT
Get PDFThe load transfer between adjacent cement concrete slabs at expansion joint locations is affected by many different factors. The load-bearing capacity of the pavement will be limited and even lead to destruction if the load transmission ability of the dowel bars does not meet the requirements. Especially, for airports that have just been put into operation or have been in operation for a long time.
In this article, the authors have researched and evaluated the effectiveness of load transfer according to deflection through the application of the 3D finite element method. The model utilizes material parameters and actual airport hard pavement structures and calculates for many types of aircraft commonly operating in Vietnam. Thereby calculating and evaluating the load transfer efficiency (LTE) according to deflection for each specific type of aircraft. The model also visually shows the deformation of the transmission dowel bars and concrete slabs at the expansion joint location. The authors tested the model's reliability through experiments conducted at Tan Son Nhat International Airport which is the largest-scale and oldest airport in Vietnam. The results of calculating LTE from the simulation and experimental models have a small error (3.39%) which shows that the model is highly reliable and can be used for similar research directions without being easily done through traditional methods
CALCULATION OF THE DRAFT OF THE FLOATING BRIDGE BUILT FROM PLASTIC BUOYS WHEN THE LOAD IS A TRUCK
Get PDFIn some emergency traffic situations such as rescue, natural disasters... it is necessary to build a temporary bridge to cross the river. Using a quick-assembled floating bridge made of plastic buoys is the appropriate solution. This article presents the study of calculating the draft of continuous floating bridge assembled from plastic buoys. The author calculates the draft by two different methods, which are theoretical calculation and finite element modeling using SAP2000 software, to verify the discrepancy of the results of these two methods. The results obtained show that the discrepancy between these two methods is insignificant, and continuous floating bridge assembled with a layer of plastic buoys can withstand a small truck load of up to 12.3 tons
EXPERIMENTAL STUDY ON THE FLEXURAL BEHAVIOR OF TRC-STRENGTHENED REINFORCED CONCRETE BEAMS
Get PDFThis paper presents the experimental results on the flexural behavior of reinforced concrete (RC) beams strengthened with textile-reinforced concrete (TRC). Four RC beams were made of B22.5 grade concrete, and the TRC strengthening layer utilized Sigratex Grid 350 textile, with fine-grained concrete Sikagrout 214-11 serving as the binder. The reinforcement layer was applied using a grooving technique. The four-point bending test was conducted to evaluate the improvements in load-bearing capacity and deformation of the beams after strengthening. The results indicated that the strengthened beams exhibited a 36.2% higher load-bearing capacity and a 13.5% increase in mid-span deflection compared to un-strengthened beams. However, the occurrence of debonding in the reinforcing layer reduced the strengthening effectiveness. To ensure the efficiency of flexural strengthening with TRC, attention should be given to the adhesion of the fine-grained concrete layer and additional reinforcement of the compression zone. These findings provide a basis for the practical application of TRC in enhancing RC structures, ensuring both safety and performance